Peroxycarboxylic acid compositions have been reported to be effective antimicrobial agents. Methods to clean, disinfect, and/or sanitize hard surfaces, meat products, living plant tissues, and medical devices against undesirable microbial growth have been described (e.g., U.S. Pat. No. 6,545,047; U.S. Pat. No. 6,183,807; U.S. Pat. No. 6,518,307; U.S. Pat. No. 5,683,724; and U.S. Patent Application Publication No. 2003/0026846). Peroxycarboxylic acids have also been reported to be useful in preparing bleaching compositions for laundry detergent applications (e.g., U.S. Pat. No. 3,974,082; U.S. Pat. No. 5,296,161; and U.S. Pat. No. 5,364,554).
Peroxycarboxylic acids can be prepared by the chemical reaction of a carboxylic acid and hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York, 1971). The reaction is usually catalyzed by a strong inorganic acid, such as concentrated sulfuric acid. The reaction of hydrogen peroxide with a carboxylic acid is an equilibrium reaction, and the production of peroxycarboxylic acid is favored by the use of an excess concentration of peroxide and/or carboxylic acid, or by the removal of water.
Some peroxycarboxylic acid-based disinfectants or bleaching agents are comprised of an equilibrium mixture of peroxycarboxylic acid, hydrogen peroxide, and the corresponding carboxylic acid. One disadvantage of these commercial peroxycarboxylic acid cleaning systems is that the peroxycarboxylic acid is oftentimes unstable in solution over time. One way to overcome the stability problem is to generate the peroxycarboxylic acid prior to use by combining multiple reaction components that are individually stable for extended periods of time. Preferably, the individual reaction components are easy to store, relatively safe to handle, and capable of quickly producing an efficacious concentration of peroxycarboxylic acid upon mixing.
One way to overcome the disadvantages of chemical peroxycarboxylic acid production is to use an enzyme catalyst having perhydrolysis activity. U.S. patent application Ser. No. 11/638,635 and U.S. Patent Application Publication Nos. 2008/0176783; 2008/0176299; and 2009/0005590 to DiCosimo et al. disclose enzymes structurally classified as members of the CE-7 family of carbohydrate esterases (i.e., cephalosporin C deacetylases [CAHs] and acetyl xylan esterases [AXEs]) that are characterized by significant perhydrolysis activity for converting carboxylic acid esters (in the presence of a suitable source of peroxygen, such as hydrogen peroxide) into peroxycarboxylic acids at concentrations sufficient for use as a disinfectant and/or a bleaching agent. Some members of the CE-7 family of carbohydrate esterases have been demonstrated to have perhydrolytic activity sufficient to produce 4000-5000 ppm peracetic acid from acetyl esters of alcohols, diols, and glycerols in 1 minute and up to 9000 ppm between 5 minutes and 30 minutes once the reaction components were mixed (DiCosimo et al., U.S. 2009/0005590).
The enzymatic peroxycarboxylic acid generation systems system described by DiCosimo et al. in each of the cited patent application publications may be based on a two-component system, where each component is stored in a separate compartment until use. Typically, the enzyme catalyst having perhydrolysis activity is stored in one compartment with the carboxylic acid ester substrate and the source of peroxygen (typically an aqueous solution use of hydrogen peroxide) is stored in a second compartment. The multiple reaction components of the two compartments are mixed to produce the desired aqueous solution of peroxycarboxylic acid.
However, multi-component enzymatic peracid generation systems may also suffer from certain problems. One problem may be the use of one or more carboxylic acid ester substrates that are insoluble or partially insoluble in water after mixing of the two components. The limited solubility of certain carboxylic acid ester substrates can result in at least three conditions that interfere with the ability to efficaciously produce and deliver a peroxycarboxylic acid product: first, the viscosity of the enzyme catalyst/substrate constituent can be too high to permit efficient mixing with a second constituent comprising a source of peroxygen, which decreases the rate of production of peroxycarboxylic acid; second, the viscosity of the enzyme catalyst/substrate constituent can be too high to permit certain modes of delivery of a product comprising a mixture of the enzyme catalyst/substrate constituent and the source of peroxygen, such as spraying; third, the dissolution rate of the substrate in the enzyme/substrate component after mixing with a second component comprising a source of peroxygen in aqueous solution is too low to permit a satisfactory rate of production of peroxycarboxylic acid. The carboxylic acid ester solubility problems also become evident in situations where use of a particular ratio of a component comprising an aqueous source of peroxygen to a component comprising an enzyme catalyst/substrate constituent is desired. As such, commercial uses of multi-component systems that involve the storage of the enzyme catalyst having perhydrolysis activity and substrate separately from a source of peroxygen until a desired time of reaction have remained impracticable for some applications.
The use of organic cosolvents to enhance mixing and/or alter the viscosity of the carboxylic acid ester in water may be problematic. Organic solvents can be deleterious to the activity of enzymes, either when enzymes are suspended directly in organic solvents, or when miscible organic/aqueous single phase solvents are employed. Two literature publications that review the effects of organic solvents on enzyme activity and structure are: (a) C. Laane et al., Biotechnol. Bioeng. 30:81-87 (1987) and (b) Cowan, D. A. and Plant, A., Biocatalysis in Organic Phase Systems., Ch. 7 in Biocatalysis at Extreme Temperatures, Kelly, R. W. W. and Adams, M., eds., Amer. Chem. Soc. Symposium Series, Oxford University Press, New York, N.Y., pp 86-107 (1992). Cowan and Plant note (on page 87) that there is little or no value in using organic solvents having a log P≦2 to stabilize intracellular enzymes in an organic phase system. Organic solvents having a log P between two and four can be used on a case-by-case basis dependent on enzyme stability, and those having a log P>4 are generally useful in organic phase systems.
Cowan and Plant, supra, further note (on page 91) that the effect of direct exposure of an enzyme dissolved in a single-phase organic-aqueous solvent depends on solvent concentration, solvent/enzyme surface group interactions, and solvent/enzyme hydration shell interactions. Because a solvent's log P value must be sufficiently low so that the solvent is fully miscible with the aqueous phase to produce a single-phase, a single-phase organic-aqueous solvent containing a low log P organic solvent usually has a negative effect on enzyme stability except in low organic solvent concentration applications.
The storage stability of a CE-7 enzyme having perhydrolysis activity is a concern when stored in a carboxylic acid ester substrate or a mixture of the carboxylic acid ester and one or more cosolvents having a partition coefficient (as measured by a log P value, i.e., the logarithm of the partition coefficient of a substance between octanol and water, where P equals [solute]octanol/[solute]water) of two or less. Several of the organic ester substrates described by DiCosimo et al. in U.S. 2009/0005590 have log P values of less than two. For example, triacetin is reported to have a log P of 0.25 (Y. M. Gunning, et al., J. Agric. Food Chem. 48:395-399 (2000)), similar to that of ethanol (log P −0.26) and isopropanol (log P 0.15) (Cowan and Plant); therefore the storage of enzyme powder in triacetin would be expected to result in unacceptable loss of enzyme activity, as would the use of additional cosolvents with log P<2 (e.g., cyclohexanone, log P=0.94) (Cowan and Plant); 1,2-propanediol, log P=−1.41 (Gunning, et al.); 1,3-propanediol, log P=−1.3 (S-J. Kuo, et al., J. Am. Oil Chem. Soc. 73:1427-1433 (1996); diethylene glycol butyl ether, log P=0.56 (N. Funasaki, et al., J. Phys. Chem. 88:5786-5790 (1984); triethyleneglycol, log P=−1.75 (L. Braeken, et al., ChemPhysChem 6:1606-1612 (2005)).
Co-owned, co-filed, and copending U.S. patent application Ser. No. 12/572,059 entitled “ENZYMATIC PERACID PRODUCTION USING A COSOLVENT” describes the use of organic co-solvents having a log P value of about 2 or less to control the viscosity of a substrate-containing component and to enhance the solubility of the substrate in an aqueous reaction mixture without causing substantial loss of perhydrolytic activity of the enzyme catalyst.
Co-owned, co-filed, and copending U.S. patent application Ser. Nos. 12/572,070 and 12/572,086 each having the title “STABILIZATION OF PERHYDROLASES”, describe various ways to stabilize enzymatic perhydrolysis activity of enzyme powders when present in the carboxylic acid ester substrate component of a multi-component peroxycarboxylic acid generation system.
Co-owned, co-filed, and copending U.S. patent application Ser. No. 12/572,094 (“IMPROVED PERHYDROLASES FOR ENZYMATIC PERACID GENERATION”) describes variant CE-7 enzymes having improved perhydrolytic activity.
The problem to be solved is to provide multi-component peroxycarboxylic acid generation formulations comprising a combination of ingredients characterized by enhanced storage stability of the CE-7 catalyst's perhydrolytic activity and/or improved mixing and/or viscosity characteristics of the carboxylic acid ester substrate-containing component. In a further embodiment, the multi-component peroxycarboxylic acid generation formulation preferably comprises a variant CE-7 enzyme having improved perhydrolytic activity